Examples of nonvolatile memory devices that use a resistance material include Phase change Random Access Memory (PRAM) devices, Resistive Random Access Memory (RRAM) devices, and Magnetic Random Access Memory (MRAM) devices. These nonvolatile memory devices store data using variations in the state of a phase change material, such as a chalcogenide alloy, variations in the resistance of a variable resistor, or variations in the resistance of a magnetic tunnel junction (MTJ) thin film with respect to the magnetization of a ferromagnetic material, whereas Dynamic Random Access Memory (DRAM) devices or flash memory devices store data using charge.
In particular, PRAM devices define a crystalline phase of a phase change material as corresponding to set data or data [0] and define an amorphous phase of a phase change material as corresponding to reset data or data [1] in consideration that a phase change material has a relatively low resistance when in the crystalline phase and a relatively high resistance when in the amorphous state. In addition, in the case of PRAM devices, a write pulse, such as a set pulse or a reset pulse, is provided to a phase change material and data is written to the phase change material with Joule heat generated by the write pulse.
Specifically, PRAM devices apply a write pulse, such as a set pulse or a reset pulse, to phase change materials and write data to the phase change materials using Joule heat generated by the write pulse. One type of PRAM device writes data [1] to phase change materials by heating the phase change materials to their melting temperature or higher using a reset pulse and quickly cooling the phase change materials so that the phase change materials become amorphous. In contrast, another type of PRAM device writes data [0] to phase change materials by heating the phase change materials to a temperature between the crystallization temperature and the melting temperature of the phase change materials using a set pulse, and then maintaining the temperature of the phase change materials for a predefined amount of time so that the phase change materials become crystalline.
Conventional PRAM devices, however, may not be able to simultaneously write a plurality of input data (e.g., 16 bits) received through a plurality of input/output (I/O) pins (e.g., 16 I/O pins) to a plurality of PRAM cells. For example, if the current of a reset pulse provided to a single PRAM cell is 1 mA, a current of 16 mA is required to simultaneously write data to 16 PRAM cells. In this case, if the operating efficiency of a write driver is about 10%, a current of 160 mA is required to simultaneously write data to 16 PRAM cells. Because the current-driving capability of PRAM devices may be limited, the number of PRAM cells to which data can be simultaneously written may also be limited.